Epsom salts, a strong laxative used in veterinary medicine, is a hydrate, which means that a certain number of water molecules are included in the solid structure. The formula for Epsom salts can be written as MgSO4 · x H2O, where x indicates the number of moles of H2O per mole of MgSO4. When 3.590 g of this hydrate is heated to 250°C, all the water of hydration is lost, leaving 1.753 g of MgSO4. What is the value of x? use correct sig digs

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The first thing we need to do is find out the molecular weight of MgSO4. When we add it up from the periodic table, we arrive at 120.37 g/mol. To see how many mols are left over at the end, we can do a quick calculation of: 1.753g/ 120.37g/mol =.0145 mols of MgSO4.

Too see how much weight the water contributed, all we do is subtract the amount of MgSO4 from the total.

Weight of H20= 3.590g - 1.753g = 1.837g of water

Next, we need to find out how many mols of water are in 1.837g. We do this by dividing it by its molecular weight: 1.837 g/ 18.02 g/mol = .1019 mols of water

lastly, in order to find the the coefficient that goes in front of H20, we divide by the smallest number:

x= .1019/.0145 = 7.030

Please let me know if you need any clarification. I'm always happy to answer your questions.

Shouldnt i just put 7 because its the formula or do i use 7.030 and would it be same for any read value and equal 7? Is it the correct amount of sig digs?

If it were me, I would just put 7 because x in this case is a coefficient in the formula, as you said.

All sig digs means is that if you were given 3 decimal places in the question, you can have that in your answer. If it is work for your teacher and he/she is strict about it, I would show my work and write: x = 7.030 , x = 7

if 7 is wrong (which i hope it wouldn't be!), I would go through the steps again and keep an extra decimal place while I'm doing the work to double check that it's 7.030, and not 7.031, for example.

I would try 7 though. - because even though you're allowed 3 sig digs in this question, it acts as a coefficient. that's my opinion...

I did it again with doing 3 sig digs for the MM instead of 2. (ie, 18.015 for water instead of 18.02, and 120.366 for MgSO4 instead of 120.37)

with that, I got .01456 mols of MgSO4, and .10197 of water. when i divided those, I got 7.003 .

(I'm not sure if your teacher wants you to do 3 sig digs the whole way through though - as in , .102/.015 = 6.8 - but that might be rounding too much.)

DId you get the same answer as me?

Jul 24th, 2015

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